Radio 1's breakfast show is no longer the most listened-to programme on British radio. That distinction belongs to Chris Evans on Radio 2. Nevertheless it's the show whose performance matters most to BBC bosses. They charged incoming Radio 1 controller Ben Cooper with lowering the station's age profile. Nothing is more important to the BBC's future than keeping a line open to the teenagers they hope will become licence fee payers. That's one of the reasons why Cooper decided it was time for Chris Moyles, 38, to be replaced by Nick Grimshaw, 28.

Out went Moyles's lugubrious monologues. In came Grimshaw's brittle patter. Out went long stretches of chat. In came music from the toppermost of the poppermost. The latest Rajar figures suggest a million listeners have taken this as a cue to move on.

Some of this is the fallout following any change. Radio is more about habit than any other branch of the media. Once you interrupt the pattern some listeners take their custom somewhere else, possibly to Evans or Christian O'Connell on Absolute, both of whom showed some growth. Nevertheless, as radio consultant Matt Deegan points out, one of the things that make Radio 1's figure skew old is the number of over-55s that still listen to it.

Some of it may be the move to a more music-heavy output. Despite the protestations of a million corny lyrics, music tends to divide people, not bring them together. Chat is something they're more likely to tolerate, even when it's provided by someone as idiosyncratic as Moyles.

There's no task in media trickier than lowering the age profile of an audience. It doesn't necessarily go down with the age of the presenter. Nor do younger people obediently respond to the promise of "younger" music. They often draw no distinction between music made today and music made on the millions of days before that. Radio 1's motto, "in new music we trust", seems addressed to an internal audience interested in positioning rather than potential listeners. The magazine graveyard is littered with the bones of titles such as Smash Hits that tried to retrace their steps to what they perceived as their core, narrowcasting themselves into obsolescence in the process.

It's been noted that these are the most pronounced falls since Matthew Bannister took over at Radio 1 in 1993 and aimed to shake off its unfortunate image. The difference now is that the radio industry, like the rest of the media, is being pushed and pulled by tides too powerful for even the most securely funded public broadcaster to resist.

Adam Bowie of Absolute Radio wrote in his blog that over the past five years radio listening among 15- to 24-year-olds has fallen by 16.9%. It's difficult to imagine those people are coming back. Anyone who lives with a teenager knows that they no longer mark their territory by retuning every radio in the house to their favourite stations. The days when they reflexively employed the radio to keep the real world at bay have gone. They can easily access all the music they want. They are never bored. Instead they are constantly distracted. Radio is just one of those competing distractions. Nothing sounds more quaint today than Lou Reed's old advice that "you need two radios in case one is broken".

The BBC's entire strategy is based on the idea that you can reliably segment the young audience via music and create channel loyalty among people who have grown up roaming free without need of channels, who pull things towards them rather than wait for somebody to do the pushing. Troy Carter, Lady Gaga's manager, recently said the last place he wanted her fans to find out about her new record was the radio, a statement which should have sent a shiver down many broadcasting spines. As one former Radio 1 hand said this week, "kids nowadays are their own schedulers. They're not going to 'keep it here' any longer."

• Thia article was amended on 20 May 2013 to correct Christian O'Connell's name